Agencies responsible for managing wildland eco systems in which accidental or natural fire is a significant concern often use long-term fire retardants in order to assist in extinguishing and controlling such fires so as to sustain only a minimum of damage. Such retardants can be applied from ground engines or aerially from helicopters and fixed wing aircraft. Fire retardants formulated for this purpose usually contain an ammonium phosphate, ammonium sulfate or mixtures thereof as the active fire retardant component. Such retardant formulations often contain, also, polygalactomannan gums to improve aerial application characteristics and cling of the fire retardant solution to the fuels on which they are applied. In addition, such formulations may contain coloring agents, corrosion inhibitors, bactericides and/or other such functional components as desired under use conditions.
One form of retardant is provided as a dry powder concentrate which, after delivery to the using location or using depot, is mixed with water and stored in a tank or tanks ready for transfer to the delivery vehicle when an emergency need arises. When these dry powder retardant concentrates are mixed with water, the polygalactomannan gum(s) which they contain are readily activated as reflected by a change in the rheological properties of the resultant solution within two to ten minutes or so after initial contact during mixing or addition is made.
Another form of retardant is provided as an aqueous fluid concentrate wherein the polygalactomannan gum and other insoluble components are suspended in a concentrated solution of the fire retardant salt(s) and auxiliary components. When suspended in high ionic strength concentrated fluids of this type, the polygalactomannan gum(s) remains inactive with no significant change in rheological properties. The concentrated fluid retardant formulations are delivered to using locations and stored as the concentrate until a fire emergency occurs. The length of storage varies dependent on the situation, e.g., from within minutes of delivery during an active emergency to the next fire occurrence which may be a year or even more in the future. Activation of the polygalactomannan gum, which is suspended in the fluid concentrate formulation, is brought about when additional water is introduced to dilute the concentrate to prepare the use-level solution. The concentrated fluids are generally not diluted until such time as the emergency occurs and they are transferred directly, following dilution, to the delivery or application vehicle. Dilution water is frequently mixed with the concentrate in the plumbing system between the storage and loading areas As with the dry-powder concentrates, the polygalactomannan gum suspended in the concentrate is activated by the dilution water resulting in the desired change in rheological properties within, at most, thirty minutes of bringing the two together.
Fire retardant solution prepared from either type of concentrate may be delivered to and applied for the intended purpose within a few minutes of being loaded or, on the other hand, the fire emergency may have changed prior to use of the diluted solution and consequently, the delivery vehicle may remain loaded or the solution may be transferred to an independent holding tank until the next need. This may be, perhaps, as long as thirty days or more after concentrate dilution and loading.
Some illustrative prior fire retardant compositions are described in U.S. Pat. No. 4,839,065; 4,971,728; and 4,983,326 all of which are incorporated herein in their entirety by reference.
In view of above described storage and use conditions, it is desired that (1) the fire retardant concentrate rapidly achieve the desired rheological characteristics so that it will perform as expected almost immediately after mixing or dilution with water and (2) the resultant fire retardant solution maintain these desirable rheological properties until use even if that does not occur for some time.
U.S. Pat. No. 3,007,879 which issued to Wesley A. Jordan on Nov. 7, 1961, addresses the loss of viscosity during storage of high viscosity aqueous guar gum solutions and discloses methods said to be useful for preventing same. The instant invention, on the other hand, addresses the rate of initial viscosity development when guar gum containing concentrates and dilution water are brought together.
Achieving and maintaining the aforementioned desirable rheological properties in a dry powder concentrate type fire retardant is possible using current technology, i.e., the polygalactomannan gum(s) remain essentially unchanged during even long term storage in the dry powder. However, the rate of viscosity development of solutions prepared from concentrated fluid type retardants often varies dependent on the length and temperature of concentrate storage prior to dilution. The rate and extent of viscosity development is one measure of the desirable rheological characteristics of fire retardant solutions. In general, viscosity development becomes progressively slower with the length of storage and increasing storage temperature. This change can be of sufficient magnitude so as to render the solution less effective in its ability to free fall from the delivery vehicles to the fuel treatment area, for example, and to cling to and protect the threatened vegetation.
In view of the emergency nature of wildland fires which occur without notice, time is critical in delivering the fire retardant solution to the fire. In order to avoid delays, the fire retardant solution must develop the desired rheological properties rapidly when needed. Any delay in ability to be readily used for any reason could make such solutions less effective than desired. Thus the invention disclosed and claimed herein is a needed improvement in this area.